The invention relates to a reflective flat-panel display device comprising a display panel which is suitable for modulating an illumination beam with image information, the display panel comprising a diffusing liquid crystalline material and a first and a second substrate enclosing the liquid crystalline material, the display device also comprising an absorbing element.
In reflective display devices having a diffusing display panel, it is relatively difficult to render the black state and the white state sufficiently black and white, respectively. Generally, the transparent state of the panel is used to realize the black state by providing an absorbing element on the side of the display panel facing away from the incident light. However, this has the result that the white state is not sufficiently bright. To obtain a bright white state, a reflector is required which reflects the light forwardly diffused by the active layer of the display panel into the viewing direction. When, for example a metallic mirror is used for this reflector, a very bright white state can be realized, but this is at the expense of the black state.
A reflective flat-panel display device of the type described in the opening paragraph is known from, for example U.S. Pat. No. 5,408,344. In the display device described in this Patent, the above-mentioned problem is solved by providing a prism plate outside the display panel. One part of the light incident on the prism plate is reflected, whereas the other part of the light will be transmitted by the prism plate so as to be subsequently absorbed by an absorbing element.
A drawback of the display device known from said United States Patent is that shadow images will occur in the case of a directed illumination. Moreover, an external reflector requires a large aperture. If the aperture is not maximal, due to, for example the presence of a black mask, the effect of the external reflector and consequently the luminance rapidly decrease. This is caused by the fact that the reflections on the glass-air interface and the external reflector occur behind the pixels so that a black mask is to be passed through twice.